The most dangerous enemy of an investor is not the market, but his own mind!

Imagine you spent weeks analyzing a company, studying its financial statements, building a valuation model, and then deciding to buy its stock. A month later, new information emerges indicating the company is facing a real problem, but instead of reconsidering your decision, you start looking for reasons to prove you were still right!

This is where the problem begins. Investors don’t always lose because of a lack of information; they may lose because they interpret information in a way that supports their existing beliefs. In behavioral finance, several mental biases influence our decisions, the most important of which are:

1. Overconfidence

Overestimating your predictions is a mistake. You might predict a stock will rise by 30% and treat that prediction as fact, even though the market is full of unpredictable factors. The problem isn’t making predictions, but forgetting that they are merely probabilities.

2. The Illusion of Control

The belief that increasing the detail of a financial model will give you greater control over the future is a misconception. You might build a valuation model with dozens of assumptions and equations, feeling that you can now accurately determine fair value. However, a more complex model cannot eliminate uncertainty; it may even make your assumptions seem more accurate than they actually are.

3. Conservatism Bias (Reservatism in Updating Beliefs)

Holding onto your old opinion despite new evidence warranting a change is a mistake. Imagine you bought a stock because the company’s profits were growing strongly, then profits started to decline and cash flow deteriorated. If you continue to rely on your old analysis, you’re not investing based on current realities, but rather defending a decision you made in the past.

4. Representativeness Bias

It’s a mistake to assume that a familiar story will end with the same result you’ve seen before. Imagine an AI company whose stock is rising rapidly; you might recall past successes in the tech industry and assume it will replicate them. But similarities in story don’t guarantee similar outcomes; profits, valuations, competition, and even the company’s survival can all differ.

What is the lesson for the investor?

Before you ask yourself, “Why do I think the stock will rise?”, ask a harder question: “What evidence can prove that I am wrong?”

Update your analysis when the facts change, don’t confuse the accuracy of calculations with the accuracy of predictions, and don’t make an attractive story a substitute for the numbers.

Ultimately, a good investor isn’t someone who always predicts the future correctly, but someone who knows the limits of their knowledge and can change their mind when the evidence changes. Protecting capital doesn’t begin with simply choosing the right investment; it also begins with recognizing the mistakes your mind might make into thinking are correct decisions.